Phenolic resins with sulfur or formaldehyde are described in U.S. Pat. No. 4,070,236 as being useful as additives for improving fine particle retention in paper manufacturing when used in conjunction with a poly(alkylene oxide) having a molecular weight of 4 to 7 million, specifically the preferred poly(ethylene oxide) (PEO) or co-condensed polyethylene/polypropylene oxide; poly(propylene oxide) is mentioned (but there would appear to be a problem of solubility with polyalkylene oxides other than poly(ethylene oxide)).
K. R. Stack, L. A. Dunn, and N. K. Roberts, show in "Study of the Interaction Between Poly(ethylene oxide) and Phenol-Formaldehyde Resin", Colloids and Surfaces (61), 1991, pp 205-218, how varying the environment and certain properties of the phenol-formaldehyde resin can affect the performance of the phenol-formaldehyde resin/PEO system. T. Lindstrom and G. Glad-Nordmark in "Network Flocculation and Fractionation of Latex Particles by Means of a Polyethyleneoxide-Phenolformaldehyde Resin Complex", J. Colloid and Interface. Science, Vol. 97, No. 1, January 1984, pp 62-67 propose a mechanism they refer to as a ". . . transient network . . . " of hydrogen bonded poly(ethylene oxide) and phenol-formaldehyde resin which swept the fine particles from the system.
The references indicate that the effectiveness of poly(ethylene oxide) for improving fine particle retention increases with its molecular weight; the effectiveness below a MW of 2 million being poor and a MW of 4 to 7 million being desirable.
However, the combination of phenol-formaldehyde resin and poly(ethylene oxide) functions less effectively as the pH is reduced below 5. The resin component also introduces formaldehyde or naphthol into the paper-making system.
There is therefore a need for a new retention aid that avoids the introduction of hazardous substances such as formaldehyde, and that can function at a lower pH, such as under 5, as well as at higher pH levels conventionally used in paper-making.